Messages in this thread Patch in this message | | | From | "Paul E. McKenney" <> | Subject | [PATCH tip/core/rcu 3/4] module: Make srcu_struct ptr array as read-only | Date | Thu, 30 May 2019 08:04:48 -0700 |
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From: "Joel Fernandes (Google)" <joel@joelfernandes.org>
Since commit title ("srcu: Allocate per-CPU data for DEFINE_SRCU() in modules"), modules that call DEFINE_{STATIC,}SRCU will have a new array of srcu_struct pointers, which is used by srcu code to initialize and clean up these structures and save valuable per-cpu reserved space.
There is no reason for this array of pointers to be writable, and can cause security or other hidden bugs. Mark these are read-only after the module init has completed.
Tested with the following diff to ensure array not writable:
(diff is a bit reduced to avoid patch command getting confused) a/kernel/module.c b/kernel/module.c -3506,6 +3506,14 static noinline int do_init_module [snip] rcu_assign_pointer(mod->kallsyms, &mod->core_kallsyms); #endif module_enable_ro(mod, true); + + if (mod->srcu_struct_ptrs) { + // Check if srcu_struct_ptrs access is possible + char x = *(char *)mod->srcu_struct_ptrs; + *(char *)mod->srcu_struct_ptrs = 0; + *(char *)mod->srcu_struct_ptrs = x; + } + mod_tree_remove_init(mod); disable_ro_nx(&mod->init_layout); module_arch_freeing_init(mod);
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk> Cc: paulmck@linux.vnet.ibm.com Cc: rostedt@goodmis.org Cc: mathieu.desnoyers@efficios.com Cc: rcu@vger.kernel.org Cc: kernel-hardening@lists.openwall.com Cc: kernel-team@android.com Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org> Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com> --- include/linux/srcutree.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/include/linux/srcutree.h b/include/linux/srcutree.h index 8af1824c46a8..9cfcc8a756ae 100644 --- a/include/linux/srcutree.h +++ b/include/linux/srcutree.h @@ -123,7 +123,7 @@ struct srcu_struct { #ifdef MODULE # define __DEFINE_SRCU(name, is_static) \ is_static struct srcu_struct name; \ - struct srcu_struct *__srcu_struct_##name \ + struct srcu_struct * const __srcu_struct_##name \ __section("___srcu_struct_ptrs") = &name #else # define __DEFINE_SRCU(name, is_static) \ -- 2.17.1
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